Preparation and characterization of cycloolefin polymer based on dicyclopentadiene (DCPD) and dimethanooctahydronaphthalene (DMON)

European Polymer Journal 49 (2013) 2680–2688

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Preparation and characterization of cycloolefin polymer based on dicyclopentadiene (DCPD) and dimethanoocta hydronaphthalene (DMON) Vania Tanda Widyaya a,b,1, Huyen Thanh Vo a,b,1, Robertus Dhimas Dhewangga Putra a,b, Woon Sung Hwang c, Byoung Sung Ahn a,b, Hyunjoo Lee a,b,⇑ a b c

Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea University of Science and Technology, Daejeon 305-355, Republic of Korea Kolon Industries, HCR Research Institute, Incheon, Republic of Korea

a r t i c l e

i n f o

Article history: Received 14 December 2012 Received in revised form 13 May 2013 Accepted 24 May 2013 Available online 5 June 2013 Keywords: Ring-opening metathesis polymerization (ROMP) Hydrogenation Dicyclopentadiene Dimethanooctahydronaphthalene Cycloolefin polymer

a b s t r a c t Ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation of the mixture of dicyclopentadiene (DCPD) and 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (DMON) were conducted. ROMP was successfully performed at room temperature using WCl6/iBu3Al/2-BuOH (1/0.7/1.2) catalyst system when the DCPD/DMON molar ratio was 1. Depending on the DCPD/DMON molar ratio, the catalyst component ratio for the polymerization changed. The double bond in the prepared ROMP polymer could be completely hydrogenated using Ni(acac)2/iBu3Al at molar ratio of the Ni/double bond in polymer = 0.2 mol% and Al/Ni = 4 when the reaction was conducted at 80 °C for 3 h. After hydrogenation, the glass transition temperature (Tg) of all ROMP polymers was decreased by 40 °C. Depending on the DCPD and DMON molar ratio, the Tg of the ROMP polymer and hydrogenated ROMP polymer changed. The hydrogenated DCPD–DMON ROMP copolymer was characterized by using 2D 1H–1H COSY and 2D 1H–13C HSQC NMR spectroscopy. Thermal stability and light transmittance for the ROMP polymer and the hydrogenated ROMP polymer were compared by using TGA and UV. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Polymers synthesized from multi-cyclo olefins such as norbornene (NB), dicyclopentadiene (DCPD), and 1,4,5,8dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (DMON) have bulky cycloaliphatic units in the polymer backbone, which provide special properties like non-crystallinity, low birefringence, high optical clarity, and low moisture absorption properties to resulting polymers. Accordingly, they are widely used as novel materials for optical lenses and prisms, high-density data-storage devices, packag⇑ Corresponding author at: Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea. Tel.: +82 29585868. E-mail address: [email protected] (H. Lee). 1 These authors equally contributed to this work. 0014-3057/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2013.05.022

ing materials for medical equipments, and as LCD film materials [1–3]. Depending on the polymerization mode, cycloolefin copolymer (COC) or cycloolefin polymer (COP) can be synthesized as depicted in Scheme 1. Addition copolymerization of cycloolefin with ethylene produce random copolymer COC, while ring-opening metathesis polymerization (ROMP) of the cycloolefin monomer produces COP [2,4]. Although the glass transition temperature (Tg) of COC can be modulated by changing the content of cycloolefin monomer, due to the high reactivity of ethylene compared to bulkier cycloolefin, Tg of COC is relatively low. However, recently, COC having a high Tg that exceeds 150 °C was reported, in which a bulkier cycloolefin based on tricyclopentadiene was used [5]. In contrast to COC, COP consists of regularly alternating cycloolefin and

V.T. Widyaya et al. / European Polymer Journal 49 (2013) 2680–2688

Scheme 1. Synthetic routes for cycloolefin copolymer (COC) and cycloolefin polymer (COP).

ethylene units. Therefore, the structure of cycloolefin determines the Tg of resulting polymer [2]. Dicyclopentadiene (DCPD) is a very attractive monomer for ROMP due to its high reactivity and low cost. However, COP based on DCPD show low Tg of 100 °C [6,7]. One way of increasing the Tg values of DCPD-based COPs to a more valuable degree is copolymerization of DCPD with bulky cycloolefin [8,9]. DMON is also a popular monomer for COP because it can be readily made from the Diels–Alder reaction of cyclopentadiene and norbornene [10]. Nevertheless, DMON-based COP is rarely investigated. The ROMP polymerization of cycloolefin should be followed by hydrogenation. Without hydrogenation, COPs have low thermal stability and low melt flow rate due to the double bond in the main chain, which makes it difficult to mold [1]. Furthermore, the hydrogenation reaction must be proceeded completely to give thermally stable polymers. Otsuki et al. reported that when the hydrogenation yield approaches 100%, the thermal stability is drastically improved [11]. Hydrogenation is also useful to improve the oxidation stability of COPs [12,13]. As a heterogeneous hydrogenation catalyst, Ni supported on clay or Pd/C has been reported [14,15]. However, because the double bond of the ring-opened polymer of multi-cycloolefin exists in the polymer main chain where bulky cycloaliphatic group exists as well, the approach of the catalyst on the reaction site is quite prohibited. Accordingly, a higher reaction temperature or a higher catalyst/ polymer ratio, as well as a longer reaction time, is required. Furthermore, deactivation of the catalyst due to the deposition of polymeric materials on the surface of the catalyst becomes a serious problem. Ziegler-type hydrogenation catalysts such as Co(neodecanoate)2 or Ni(2-ethylhexanoate)2 with AlEt3 constitute one of the most important families of industrial hydrogenation catalysts, especially for polymer hydrogenation catalysts such as styrene block copolymers [16,17]. Accordingly, numerous studies have focused on optimization of the process, including the catalyst synthesis step, starting components, and methods. At the same time, many observations have reported on how the catalyst synthesis variables affect the activity of the resulting hydrogenation

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catalyst [16]. From this point of view, it is worth investigating the optimal hydrogenation conditions for ROMP polymers, as these have not been examined in detail yet. In this paper, we report on the synthesis of ring-opening metathesis copolymers of DCPD–DMON (p-DCPD– DMON) with various molar ratios of DCPD/DMON and on the hydrogenation for the syntheses of hydrogenated ROMP copolymers (H-p-DCPD–DMON) (Scheme 2). As catalysts for ROMP and hydrogenation, we used the commercially available and the industrially applicable catalyst systems comprised of WCl6/iBu3Al/2-BuOH and Ni(acac)2/ iBu3Al, respectively. We attempted to find the optimal reaction condition as well as the best catalyst composition for each reaction condition. Furthermore, the synthesized polymers were characterized by using NMR, GPC, DSC, UV and TGA. 2. Experimental 2.1. Materials All reagents except DMON were purchased from Sigma– Aldrich Chemicals Co. DMON was donated from Kolon Industry. All reagents were anhydrous grade and distilled after Na/K alloy treatment if required. Water content in all reagents was less than 10 ppm. 2.2. ROMP of DCPD–DMON (p-DCPD–DMON) ROMP reaction was conducted inside glove box (O2 < 1 ppm and H2O < 1 ppm) in the same way as previously reported [18,19]. In a 100 mL round bottomed flask, a desired amount of DCPD and DMON (35 mmol total) was mixed with an anhydrous cyclohexane. The concentration of monomer/solvent was 10 wt%. Into this solution, 0.35 mmol of 1-hexene (0.3 M in cyclohexane), 0.025 mmol of iBu3Al (0.05 M in cyclohexane), 0.042 mmol of 2-BuOH (0.05 M in cyclohexane), and 0.035 mmol of WCl6 (0.01 M in cyclohexane) were added successively with stirring. The solution was stirred for 2 h at room temperature until dark yellow viscous solution was formed (pDCPD–DMON). Then, the polymer solution was poured into large amount of 2-butanol and separated the white precipitates by using filtration. p-DCPD–DMON solid was dried under vacuum overnight. The yield of isolated polymer was over 99%. 2.3. Hydrogenation of p-DCPD–DMON (H-p-DCPD–DMON) Hydrogenation catalyst was prepared by mixing 10 mg Ni(acac)2 (0.04 mmol), 3 mL anhydrous cyclohexane as solvent, and 0.16 mmol of iBu3Al (1 M soln. in hexane) successively. The less soluble green Ni(acac)2 started to dissolve by the reaction with iBu3Al and the solution turned into dark black color. This catalyst solution was stirred for 2 min. Polymer solution was prepared by dissolving 2 g of p-DCPD0.5–DMON0.5 (polymer obtained from DCPD/ DMON = 1/1 M ratio) powder (total 20.5 mmol of double bond) in 20 mL of anhydrous cyclohexane. Prepared

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DCPD

n

ROMP cat.

+ DMON

m

p-DCPD-DMON

H2 cat.

n

m

H-p-DCPD-DMON

Scheme 2. Ring-opening metathesis polymerization (ROMP) and hydrogenation of DCPD–DMON.

polymer solution was mixed with prepared catalyst solution (0.04 mmol of Ni) in 100 mL bomb reactor. The reactor was flushed with hydrogen three times and then pressurized with 34 bar of hydrogen. The hydrogenation reaction was conducted at 80 °C. After 3 h, the reactor was cooled down to room temperature and the hydrogen gas was vented off. After hydrogenated ROMP polymer (H-pDCPD–DMON) solution was treated with activated carbon for the removal of metal residue, it was precipitated using a large amount of 2-butanol. Isolated white powder was dried under vacuum overnight. The degree of hydrogenation was measured by using 600 MHz 1H NMR. 2.4. Characterization of p-DCPD–DMON and H-p-DCPD– DMON The copolymerization between DCPD and DMON was analyzed by using 600 MHz 1H NMR and 150 MHz 13C NMR spectroscopy (Bruker Avance 600). The chemical structure of H-p-DCPD–DMON was characterized by using 1 H NMR, 13C NMR, 13C distortionless enhancement by polarization transfer (DEPT), two-dimensional homonuclear correlation spectroscopy (2D 1H–1H COSY), and twodimensional heteronuclear single quantum coherence (2D 1 H–13C HSQC). C6D12 was used as a solvent to dissolve the p-DCPD–DMON while CCl4 and CDCl3 were used as a solvent to dissolve H-p-DCPD–DMON for NMR measurement. Gel permeation chromatography (Younglin) with RI detector (RI-750F, Younglin) was used to measure the molecular weight and polydispersity. For the analysis of the polymers, two PSS SDV linear M 5 lm columns (8  300 mm, PSS USA) were connected and cyclohexane was used as an eluent. The operation temperature and the flow rate of eluent were set at 25 °C and 0.5 mL/min, respectively. Monodisperse polyisobutylene was used as a standard sample to make a calibration curve. The glass transition temperature (Tg) was measured by using differential scanning calorimeter (Q10, TA Instruments) supported with refrigerated cooling system. The heating rate was 10 °C/min from 20 °C to 300 °C under nitrogen. The decomposition temperature was determined by using thermogravimetric analysis (SDT 2960 Simultaneous DTA–TGA, TA Instruments). The heating rate was 10 °C/ min from room temperature to 600 °C under nitrogen. The light transmittance was measured by using UV (Cary 5000, Varian) at the range of 200–850 nm. Polymer film was made by dissolving 0.5 g of hydrogenated polymer powder in 4.5 g methylcyclohexane. The solution was poured into 10 cm ID petri dish. The slow evaporation of solvent left a smooth transparent film with a thickness of 60 lm.

3. Results and discussion 3.1. ROMP of DCPD–DMON Although a few decades have passed since the invention of the WCl6–trialkylaluminum–ROH-based catalyst system, it is still regarded as an ill-defined catalyst system [20]. Furthermore, due to the immediate reaction with moisture and oxygen, all catalyst components and reagents for the ROMP reaction should be handled in strictly controlled Argon atmosphere glove box. Nevertheless, due to its high catalytic activity, commercial accessibility, and economic advantages, the WCl6–trialkylaluminum–ROH mixture is considered as a feasible catalyst for industrialscale production of COPs. In this paper, we synthesized three different types of copolymers having different DCPD/DMON ratios of 3/1 (p-DCPD0.75–DMON0.25), 1/1 (p-DCPD0.5–DMON0.5), and 1/ 3 (p-DCPD0.25–DMON0.75) as well as DCPD (p-DCPD) and DMON (p-DMON) single-component polymers. WCl6/iBu3Al/2-BuOH was used as the catalyst system and the molar ratio of monomer to WCl6 was fixed at 1000. In addition, the molar ratio of monomer to 1-hexene as a molecular weight controller was fixed at 100. Table 1 shows the effects of DCPD–DMON molar ratio and catalyst composition on the ROMP. The polymerization condition was optimized using the DCPD/DMON 1/1 mixture (p-DCPD0.5–DMON0.5). As shown in entries 3–1, 3–2, and 3–3, increasing the amount of 2-BuOH from 1.2 to 2 equiv. with respect to the amount of WCl6 resulted in the decreasing of gel formation with a lower yield of polymer, but further increasing of 2-BuOH to 3 equiv. poisoned the catalyst activity. The optimum catalyst composition for DCPD0.5–DMON0.5 was obtained by decreasing iBu3Al to 0.7 equiv. and keeping 2-BuOH at 1.2 equiv. (entry 3–4). When this optimum ROMP condition of DCPD0.5–DMON0.5 (monomer/1-hexene/iBu3Al/2-BuOH/WCl6 = 1000/10/0.7/ 1.2/1) was employed to DCPD0.75–DMON0.25 (entry 2–1), the yield of polymer was only 68% with 15.6% of gel content. The optimum catalyst composition for DCPD0.75– DMON0.25 was 0.5 equiv. of iBu3Al and 1 equiv. of 2-BuOH with respect to the amount of WCl6 (entry 2–2). In the case of DCPD, more than 95% gelated polymer was observed when iBu3Al/2-BuOH was 0.7/1.2 (entry 1–1). Instead, the optimum catalyst composition for DCPD was 0.5/1 of iBu3Al/2-BuOH (entry 1–2). Whereas, DCPD0.25–DMON0.75 (entry 4) and DMON (entry 5) showed 100% polymerization yields without forming gel when WCl6/iBu3Al/2BuOH = 1/0.7/1.2. Although the exact catalyst structure formed from the reaction of WCl6/iBu3Al/2-BuOH remains unclear, we could discern the tendency of this polymerization. That is,

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Table 1 ROMP of various DCPD–DMON compositions using WCl6/iBu3Al/2-BuOH catalyst system. Entry

Monomer

iBu3Al/ WCl6

2BuOH/ WCl6

Yield of polymer (%)

Gel content (%)

1–1 1–2 2–1

DCPD DCPD DCPD0.75– DMON0.25 DCPD0.75– DMON0.25 DCPD0.5– DMON0.5 DCPD0.5– DMON0.5 DCPD0.5– DMON0.5 DCPD0.5– DMON0.5 DCPD0.25– DMON0.75 DMON

0.7 0.5 0.7

1.2 1 1.2

100 100 68

>95 0 15.6

0.5

1

100

0

1

1.2

100

>95

1

2

70

1

3

0

0

0.7

1.2

100

0

0.7

1.2

100

0

0.7

1.2

100

0

2–2 3–1 3–2 3–3 3–4 4 5

4.8

increasing the alcohol concentration led to a low polymerization yield, while decreasing the alcohol concentration led to gel formation. Conversely, increasing the iBu3Al concentration led to gel formation and decreasing the iBu3Al concentration led to a low polymerization yield. Table 1 also shows the gelation happens predominantly at the DCPD-rich compositions. Davidson et al. reported the double bond in five-membered ring of DCPD is inactive toward ROMP, but it can join addition polymerization at certain reaction environment such as high temperature reaction condition [21]. In our reaction, the presence of excess amount of iBu3Al could induce cationic polymerization on the five-membered ring site as well as norbornene site of DCPD, which resulted in the gel formation. Or, like the case of the research by T. A. Davidson et al., highly active catalyst species which might be formed under the iBu3Al-excess condition could give rise to large amount of local heat during the ROMP reaction, causing the addition polymerization of double bond in five-membered ring of DCPD.

Fig. 1. Effect of iBu3Al/Ni(acac)2 molar ratio on the hydrogenation of pDCPD0.5–DMON0.5. Reaction condition: polymer 2 g, Ni(acac)2 20 mg, 34 bar H2, 80 °C, 6 h.

Fig. 2. Effect of reaction time on the hydrogenation of p-DCPD0.5– DMON0.5. Reaction condition: polymer 2 g, Ni(acac)2 20 mg, iBu3Al/ Ni(acac)2 = 4, 34 bar H2, 80 °C.

3.2. Hydrogenation of p-DCPD–DMON p-DCPD–DMON hydrogenation was conducted using a catalyst system prepared from Ni(acac)2 and iBu3Al. The role of iBu3Al is to reduce Ni(II) to Ni(0) [17]. However, if the amount of iBu3Al is higher than the required amount, the excess iBu3Al can induce polymerization, which can then result in gel formation. We investigate the optimum composition between Ni(acac)2 and iBu3Al necessary to obtain the complete hydrogenation of the ROMP polymers using p-DCPD0.5–DMON0.5 prepared at its optimal polymerization composition (Monomer/1-hexene/iBu3Al/2-BuOH/WCl6 = 1000/10/0.7/1.2/1). The hydrogenation reaction was conducted at 80 °C under 34 bar of H2 pressure. Fig. 1 shows that when the molar ratio of Al/Ni was less than 2, the hydrogenation was poorly preceded. However, when the Al/Ni ratio was 2, the hydrogenation yield increased rapidly and reached 100% when the Al/Ni ratio was higher than 2.5. A further increase of iBu3Al to more

Fig. 3. Effect of Ni(acac)2/double bond in p-DCPD0.5–DMON0.5 molar ratio on the hydrogenation of p-DCPD0.5–DMON0.5. Reaction condition: polymer 2 g, iBu3Al/Ni(acac)2 = 4, 34 bar H2, 80 °C, 3 h.

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Fig. 4. (a) 1H NMR and (b)

13

C NMR spectra of p-DCPD0.5–DMON0.5 and H-p-DCPD0.5–DMON0.5.

than 5 gave rise to the gelation of the ring-opened polymer by simply mixing the catalyst solution with the polymer solution, indicating that an excessive amount of iBu3Al was used. Therefore, the molar ratio of iBu3Al/Ni(acac)2 was fixed at 4, as this composition resulted in a stable 100% hydrogenation yield in less time than a molar ratio of 3 as described hereafter. In Fig. 2, the effect of the reaction time on the hydrogenation of the ring-opened polymer is depicted. It can be concluded that the minimum reaction time required to

obtain a 100% hydrogenation yield was 3 h when the iBu3Al/Ni(acac)2 molar ratio was 4. However, when the iBu3Al/ Ni(acac)2 molar ratio was 3, a 3 h reaction only resulted in a 90% hydrogenation yield. After setting the molar ratio of iBu3Al/Ni(acac)2 to 4, the effect of the amount of Ni(acac)2 was investigated. As shown in Fig. 3, when the reaction was conducted for 3 h, the molar ratio of Ni to the double bonds in p-DCPD0.5– DMON0.5 should be at least 0.2 mol% for complete hydrogenation.

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Fig. 5.

13

2685

C NMR spectra of H-p-DCPD, H-p-DMON, and various H-p-DCPD–DMON.

When the optimum hydrogenation reaction condition of p-DCPD0.5–DMON0.5 was applied to all of the prepared polymers (Al/Ni = 4, Ni/double bond in polymer = 0.2 mol%, 80 °C, 3 h, 34 bar H2), they also showed complete hydrogenation yields.

3.3. NMR analyses Degree of hydrogenation of p-DCPD, p-DMON, and the three types of p-DCPD/DMON could be measured by using 1 H and 13C NMR. As shown in Fig. 4a, the double-bond protons of p-DCPD0.5–DMON0.5 which appeared at 5–6 ppm disappeared completely after the hydrogenation. The double-bond carbons of p-DCPD0.5–DMON0.5 (125–135 ppm) also disappeared upon hydrogenation (Fig. 4b). Other polymers of p-DCPD, p-DMON and the copolymers of DCPD and DMON hydrogenated completely at the same condition (Figs. S1–S4 in Supporting information). Furthermore, the 13C NMR spectra of the hydrogenated polymers showed that the intended copolymerization of DCPD and DMON was successful. As shown in Fig. 5, for H-p-DCPD–DMON, the peaks appearing at 27.6, 28.2, 30.3, 36.6, 42.98, and 45.7 ppm correspond to H-p-DCPD while the peaks appearing at 29.9, 30.6, 36.6, 37.01, 41.3, 43.36, and 51.5 ppm correspond to H-p-DMON. Depending on the molar ratio of the DCPD and DMON, the peak intensity changed. The structure of H-p-DCPD0.5–DMON0.5 was characterized by using 2D 1H–13C HSQC, 2D 1H–1H COSY and 13CDEPT NMR spectroscopy (Fig. 6 and Fig. S5 in Supporting information for 13C-DEPT). Based on 13C-DEPT, the peaks

appearing at 27.6–30.6, 36.6, and 41.3 ppm could be assigned as methylene group and peaks appearing at 37.01 and 42.98–51.5 ppm could be assigned as methine group. Furthermore, based on the 1H and 13C NMR spectra of Hp-DCPD and H-p-DMON, each peak in the 2D-NMR spectrum could be clearly distinguished. Through an analysis of the coupling between the 1H–13C NMR spectra in the 2D 1H–13C HSQC and the 1H–1H NMR spectra in the 2D 1 H–1H COSY, all proton and carbon signals could be assigned, as shown in Fig. 6.

3.4. Characterization By using a gel permeation chromatography, the Mw and PDI were measured. Table 2 reveals that all hydrogenated COPs have a Mw ranging from 3.9  104 to 5.9  104 and PDI in the range of 2.4–2.8. The profiles of GPC analysis was shown in Fig. S6 in Supporting information. The effect of the DCPD–DMON composition towards Tg values of p-DCPD–DMON and H-p-DCPD–DMON was examined by using DSC and the results are shown in Table 2, Fig. 7 and Figs. S7 and S8 in Supporting information. The Tg of the ring-opened DCPD polymer was 146 °C, which is similar to the value in the previous report [9,12]. With increasing the content of DMON to 25 mol%, the Tg values of the copolymers also gradually increased and reached to 206 °C at p-DCPD0.25–DMON0.75, which is similar to the Tg of p-DMON. Table 2 and Fig. 7 also show that the Tg values of the prepared polymers were decreased by 35–55 °C after the hydrogenation due to the increase in mobility and chain

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Fig. 6. (a) 2D 1H–13C HSQC and (b) 2D 1H–1H COSY of H-p-DCPD0.5–DMON0.5.

rotation compared to the double bond-containing polymers. As a result, it was concluded that the Tg values of COP polymers could be controlled in the range between 102 and 174 °C by changing the molar ratio of DCPD/ DMON. On the other hand, the DSC thermograms did not show the presence of melting temperature both in p-DCPD–DMON and H-p-DCPD–DMON, indicating that both p-DCPD–DMON and

H-p-DCPD–DMON are amorphous polymers (see Figs. S7 and S8 in Supporting information). The thermal decomposition temperatures of p-DCPD, pDMON, and p-DCPD–DMON based on 5% weight loss were measured by using TGA and the results are shown in Fig. 8 and Fig. S9 in Supporting information. Interestingly, the polymers formed from the DCPD–DMON mixture showed a higher decomposition temperature (400 °C) than the

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Table 2 Characteristics of H-p-DCPD, H-p-DMON, and various H-p-DCPD–DMON.

a

Entry

DCPD–DMON

Mw ( 104)

PDI

Tg (°C)

1 2 3 4 5

DCPD DCPD0.75–DMON0.25 DCPD0.5–DMON0.5 DCPD0.25–DMON0.75 DMON

5.2 3.9 4.2 5.5 5.9

2.8 2.5 2.5 2.4 2.4

102 118 135 164 174

(146)a (172)a (188)a (206)a (209)a

Before hydrogenation.

Fig. 9. Light transmittances of p-DCPD0.5–DMON0.5 and H-p-DCPD0.5– DMON0.5.

Fig. 7. Glass transition temperatures of COPs with various DCPD/DMON molar ratios.

decomposition of the ring-opened polymers occurred at a lower temperature, around 400 °C, but did not finish, even at 600 °C, presumably due to the formation of char. Interestingly, the thermal stability of the DCPD polymer was greatly improved upon hydrogenation, as indicated by the increase in the decomposition temperature from 381 °C to 436 °C which makes it have decomposition temperature similar to those of the hydrogenated copolymers of DCPD–DMON. This higher thermal stability of H-p-DCPD compared to the other polymers could be ascribed to its thermodynamically stable saturated five-membered ring structure. Hydrogenation was also effective for improving the light transmittance of COPs, as shown in Fig. 9. p-DCPD0.5– DMON0.5 showed a quite high light transmittance at a wavelength longer than 600 nm; however, at the wavelength light shorter than 500 nm, the light transmittance decreased rapidly. In contrast, the hydrogenated polymer, H-p-DCPD0.5–DMON0.5, showed high light transmittance of 92% at 400 nm. 4. Conclusions

Fig. 8. Decomposition temperatures of COPs with various DCPD/DMON ratios.

single-component ring-opened polymers of DCPD (381 °C) and DMON (378 °C). In addition, upon hydrogenation, the thermal stability of the polymers was further enhanced to more than 420 °C and the decomposition finished completely at a temperature below 500 °C, whereas the

Ring-opening copolymerization of various molar ratios of DCPD/DMON was successfully conducted using WCl6/ iBu3Al/2-BuOH catalyst system. The molar ratio of the catalyst components for a ROMP reaction without gel formation was found to depend on the DCPD/DMON molar ratio. For p-DMON, p-DCPD0.25–DMON0.75, and p-DCPD0.5– DMON0.5, optimal catalyst composition was monomer/ WCl6/iBu3Al/2-BuOH = 1000/1/0.7/1.2. Meanwhile, for a higher DCPD composition such as p-DCPD0.75–DMON0.25 and p-DCPD, less amount of iBu3Al was required for the prevention of gelation. Complete hydrogenation of ROMP polymers could be accomplished at molar ratio of the Ni/ double bond in p-DCPD–DMON = 0.2 mol% and Al/Ni = 4. Upon hydrogenation, the thermal stability and light transmittance of copolymers were drastically improved. As a result, by changing the molar ratio of DCPD/DMON, the Tg value of the cycloolefin polymers could be modulated between 100 and 170 °C.

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